Excimer lamp and light irradiation device

An excimer lamp, comprising

• a discharge vessel;
• and
• a pair of electrodes arranged on an outer surface of the discharge vessel,
• wherein an interior of the discharge vessel is filled with
• a first gas comprising krypton (Kr);
• a second gas comprising chlorine (Cl) or bromine (Br);
• and
• a third gas which is at least one species selected from among the group consisting of argon (Ar), neon (Ne), and helium (He), a partial pressure Pb of the third gas being not less than a partial pressure Plg of the first gas,
• wherein the excimer lamp satisfies Pb/Plg 10.0,
• wherein where the second gas includes chlorine (Cl), an ultraviolet light having a primary peak wavelength of 222 nm radiates by the excited dimers of KrCl*, and
• wherein where the second gas includes bromine (Br), an ultraviolet light having a primary peak wavelength of 207 nm radiates by the excited dimers of KrBr*.